In the processing of semiconductor devices, such as transistors, diodes, and integrated circuits, a plurality of such devices are typically fabricated simultaneously on a thin slice of semiconductor material, termed a substrate, wafer, or workpiece. When manufacturing such semiconductor devices, it is desirable that the wafer does not become contaminated by particulates, which may lead to device failure. Accordingly, wafer processing systems typically include a multi-wafer load lock apparatus that provides a substantially particle free environment into which a batch or “lot” of wafers may be inserted while waiting to be processed. After wafers are loaded into the load lock, the load lock is evacuated to remove any particulates. The load lock is then backfilled with a purified gas, for example an inert gas, either to the ambient pressure or to a reduced pressure. A single wafer or a plurality of wafers may then be selectively withdrawn from the load lock for placement into one or more processing modules without opening the load lock to the ambient environment. After processing of the wafers in the process module and placement back into the load lock, the load lock is backfilled to ambient pressure, if necessary, and opened to the ambient environment. The wafers are then unloaded and the process is repeated.
An auxiliary process may be performed on a wafer in an auxiliary processing module before or after it is processed in a main processing module. Examples of such auxiliary processing include measuring, testing or cleaning the wafer before or after the main wafer processing has been performed on the wafer in a main process module, to further improve the quality of the processing of the wafer, or of subsequent wafers. In systems comprising a traditional multi-wafer load lock, at least one wafer is typically removed from the load lock and transported to an off-line tool or side chamber to undergo such auxiliary processing. To remove the wafer for auxiliary processing, the entire load lock is brought to atmospheric pressure before a loading port can be opened. Once the port is opened, all of the wafers in the load lock are exposed to the ambient environment, which can be detrimental in certain processing applications by introducing particulates into the load lock from the ambient environment. Backfilling and re-evacuating of the load lock every time a wafer is removed for auxiliary processing, whether before or after main processing, also results in low throughput, which is the number of wafers that are processed in a certain period of time.
Accordingly, a need exists for a load lock apparatus that will allow at least one wafer to be processed in an auxiliary process chamber without prematurely exposing the remaining wafers to the ambient environment and without reducing the throughput of wafers.